This invention relates to solvent based coating compositions and in particular to a clear coating composition for refinishing clear coat/color coat finishes of vehicles, such as, automobiles or trucks. Also, the coating composition can be pigmented and used to refinish mono-coated vehicles.
Clear coat/color coat finishes for automobiles and trucks have been used in recent years and are currently being used. Typically, such finishes are produced by a wet-on-wet method, in which the color coat or basecoat which is pigmented is applied and flash dried for a short period of time but not cured and then the clear coat, which provides protection for the color coat and improves the appearance of the overall finish, such as, gloss and distinctness of image, is applied thereover and both the color coat and the clear coat are cured together.
Repair of such clear coat/color coat finishes that have been damaged, e.g., in a collision, has been difficult in that the clear coat refinish compositions in current use, for example, as taught in Corcoran et al. U.S. Pat. No. 5,279,862, issued Jan. 18, 1994, Lamb et al. U.S. Pat. No. 5,286,782, issued Feb. 15, 1994, Anderson et al. U.S. Pat. No. 5,354,797, issued Oct. 11, 1994, and Huynh-Ba U.S. Pat. No. 6,472,493 issued Oct. 29, 2002 have acceptable drying times suitable for automotive refinish, i.e., to a dust free state, but nonetheless take many hours to cure to a sufficiently hard and water resistant state at ambient or slightly elevated temperatures. As a result, the vehicle cannot be moved outside of the autobody repair facility to free work space in the autobody repair facility without the risk of water spotting nor can the clear coat be sanded (wet or dry) or buffed to a high gloss finish on the same day of application. Thus, the productivity of a refinish operation is still lacking, since the vehicles cannot be stored outside or worked on quickly after application of the finish.
One approach used to improve the initial hardness and water resistance of a clear coat composition on curing involves the use of high levels of a tin catalyst; however, such high levels produce certain unwanted side effects, such as, reduced pot life and increased “die-back”. Die-back mainly occurs as the film is formed before all solvents are evaporated. The solvents that are trapped create a stress on the film as they eventually flash away, which distorts or wrinkles the film and converts it almost overnight from an attractive high gloss mirror-like finish into a film having a dull fuzzy appearance and poor gloss and distinctness of image.
A continuing need still exists for a coating composition, preferably, a low VOC (Volatile Organic Content) coating composition, suited for use as a clear coat in automotive refinishing that offers high film hardness and water resistance in a very short period of time when cured at ambient or slightly elevated temperatures, with little or no pot life reductions and die-back consequences, so that a vehicle can be moved or worked on quickly after application of the coating composition.